Rails & MySQL on Apple Silicon

I've had success with just the following:

rbenv exec gem install mysql2 -- \
--with-mysql-lib=/opt/homebrew/Cellar/mysql/8.0.25_1/lib \
--with-mysql-dir=/opt/homebrew/Cellar/mysql/8.0.25_1 \
--with-mysql-config=/opt/homebrew/Cellar/mysql/8.0.25_1/bin/mysql_config \
--with-mysql-include=/opt/homebrew/Cellar/mysql/8.0.25_1/include 

(Note that you may need to change the version number in those paths)

Notably, this worked with the most recent version of mysql and does not require any Intel versions or using an emulated version of HomeBrew (e.g. ibrew).

Configure Bundler to use this build configuration automatically:

You may also want to set this configuration as your default for mysql2. This way anytime bundler has to re-install mysql2 (on this project or any other project on the same computer), it will automatically use this configuration. You can do that with the following:

bundle config set --global build.mysql2 \
--with-mysql-lib=/opt/homebrew/Cellar/mysql/8.0.25_1/lib \
--with-mysql-dir=/opt/homebrew/Cellar/mysql/8.0.25_1 \
--with-mysql-config=/opt/homebrew/Cellar/mysql/8.0.25_1/bin/mysql_config \
--with-mysql-include=/opt/homebrew/Cellar/mysql/8.0.25_1/include 

Based on @matthias-winkelmann's answer, use brew to find the correct version of mysql for you:

gem install mysql2 -v '0.5.3' -- \
--with-mysql-lib=$(brew --prefix mysql)/lib \
--with-mysql-dir=$(brew --prefix mysql) \
--with-mysql-config=$(brew --prefix mysql)/bin/mysql_config \
--with-mysql-include=$(brew --prefix mysql)/include 

Do notice the specific version of the mysql2 gem I'm referring to here.